In the production of silicon wafers, a mask is typically utilized as a contact mask to provide a pattern of tin lead contacts. To form the tin lead contacts on the wafer, a mask is applied to the wafer, and the mask-wafer composite is exposed in a tin lead evaporation chamber. Tin lead is evaporated through the holes in the mask onto the wafer and the pattern of the holes in the mask dictates the pattern of the tin lead contacts.
As a result of this process, the tin lead forms a bond of solder between the mask and wafer. The tin lead bonds partially cover the opposite facing surfaces of the mask and wafer, i.e., extent of coverage depends on the mask pattern. The conventional technique for removing the mask from the wafer is to manually peel the mask from the wafer.
Manual peeling the mask from the wafer is an operator dependent procedure. Thus, controlled, uniform, and repeatable results are not readily obtainable. The major yield problem caused by this manual process are that when operators peel the masks from the wafers, they cause damage to either the mask or wafer or both. This damage decreases wafer yields, and in addition increases the cost of the final product because masks that are normally cleaned and reused are damaged so that they cannot be reused.
To increase wafer yields and the reutilization of masks, meticulous operator handling is required. This results in increased process times, labor costs and training costs. Moreover, substantially improved results are not guaranteed with meticulous operator handling. Thus, utilization of known means and methods to remove masks from wafers after tin lead evaporation results in damage to wafers and masks resulting in decreased yields, increased cost and process time. Therefore, it is a primary object of this invention to provide a means for removing a mask from a wafer without damaging the mask or wafer.
It is a further object of this invention to provide a means for removing a mask from a wafer that is not operator dependent.
It is a further object to provide a controlled, uniform, repeatable method of removing masks from wafers.